Today's confirmation that Apple is going x86 makes today a historic day in the industry. It may mean that Microsoft might see a few percent decline of their market share the next few years, but what about Linux? If Linux were to lose an equal amount of share it would alter its spread to the desktop, a spread that has been very positive so far.

Not too likely. MS hasn't done it, Apple won't do it either. They cater to very different user markets. Also keep in mind that server space will still have a foothold with Linux / BSD. Apple has been trying to get into the server market but they don't have the credibility.